This invention relates to catheter introducers, i.e. to a device which enables the introduction of a catheter, guide wire or the like into a patient's vasculature.
Catheter introducers are used to assist in the introduction of catheters or guide wires into a patient's vascular system (typically an artery) for many different types of intravascular procedures. The introducer (and its associated dilator) must penetrate the skin and wall of the blood vessel and be positioned within the blood vessel so that catheters can be advanced and withdrawn through the introducer. In this way even when multiple catheters or guide wires are required, injury to the patient is limited to the single placement of the introducer through the skin and vessel wall.
For a number of reasons, it is desirable to minimize the outer diameter or profile of an introducer sheath. For one, obstruction of blood flow in the blood vessel is reduced. This is an important consideration in pediatric procedures and when it is necessary to introduce catheters through the arm. Also, a smaller outer diameter reduces the trauma suffered by the patient, and, consequently, the patient's recovery time.
It has been recognized that a thin walled sheath is beneficial. One such introducer sheath known as a Desilets-Hofmann arterial sheath comprised a very thin wall (0.003 inches) which was made by spiral wrapping Mylar.TM. polyester tape on a mandrel to insure good diameter tolerances and roundness. The edges of the tape are overlapped and bonded with adhesive to yield a cylindrical tube. The tube was then spray coated with a thermoset polyurethane and the tip ground to provide an external taper. The product is no longer on the market.
Currently available catheter introducer sheaths are made from tubing which is manufactured by extrusion. Extrusion is a low cost manufacturing process but results in tubing having a relatively high variation in inner diameter and roundness. Since the introducer sheath must be able to accommodate the outer diameter of the catheter which is to be introduced, a relatively large inner diameter must be specified for an extruded introducer sheath. Accordingly, in the manufacture of known catheter introducers, the extruded tube is heat treated to bring the inner diameter of its distal tip to the more precise values required for a specified catheter. In this way, at least the diameter of the distal tip is minimized.
Another factor which affects the outer diameter or profile of an introducer sheath is the thickness of the wall of the sheath. Conventionally, introducer sheaths are made of polytetrafluoroethylene (PTFE), polyethylenebutylacrylate (PEBA), and polyethelene. The introducer sheath must be stiff enough that it will not kink when it is pushed through the skin and into the blood vessel with the assistance of a dilator. For such materials, typical wall thickness ranges from 0.007 inches to 0.010 inches.